A well known part of the process of manufacturing semiconductor integrated circuits is the manufacturing of resistors in semiconductor integrated circuits. FIG. 1 illustrates pertinent portions of a prior art process of manufacturing a resistor in a semiconductor integrated circuit. A region of a semiconductor substrate D, for example a silicon substrate, has implanted therein a dopant, for example a P+ dopant such as Boron, to form a doped semiconductor region (diffusion resistor) B. The dopant is implanted through a thin (e.g., 7 nm) screen oxide A. The resulting structure is subsequently subjected to an annealing process, for example a Rapid Thermal Anneal process.
FIG. 2 graphically illustrates an example of an anneal recipe used in a prior art Rapid Thermal Anneal process. FIG. 2 illustrates gas flow 21 and temperature 23 versus time. The gas flow is shown in liters per minute (LPM), and the temperature is shown in degrees centigrade (° C.). In the example of FIG. 2, the gas flow illustrated at 21 is a nitrogen (N2) gas flow. Depending on the particular integrated circuit that is being manufactured, and the particular manufacturing process that is being employed, the use of nitrogen gas flow in the wafer processing tool during the anneal step can be preceded by the use of various other types of process gases in the wafer processing tool during performance of earlier steps of the manufacturing process. This is illustrated generally in FIG. 3, where any of the process gases illustrated at 33 can be utilized in steps which precede the use of nitrogen process gas in the anneal step at 31. In FIG. 3, the possible predecessor gases shown at 33 are nitrogen, ammonia (NH3) and oxygen (O2). Various other process gases could also be used in the wafer processing tool during manufacturing steps which precede the nitrogen-based anneal step 31.
One important parameter in manufacturing resistors in semiconductor integrated circuits is the distribution of the actual resistance values of the manufactured resistors with respect to the target or desired resistance value. A tighter distribution results in a higher usable yield and more competitive pricing.
It is desirable in view of the foregoing to provide for a tight distribution of resistance values when manufacturing resistors in semiconductor integrated circuits.